From: Peter Collingbourne <pcc@google.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Peter Collingbourne <pcc@google.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: [PATCH] arm64: mte: optimize asynchronous tag check fault flag check
Date: Tue, 17 Nov 2020 19:20:51 -0800 [thread overview]
Message-ID: <20201118032051.1405907-1-pcc@google.com> (raw)
We don't need to check for MTE support before checking the flag
because it can only be set if the hardware supports MTE. As a result
we can unconditionally check the flag bit which is expected to be in
a register and therefore the check can be done in a single instruction
instead of first needing to load the hwcaps.
On a DragonBoard 845c with a kernel built with CONFIG_ARM64_MTE=y with
the powersave governor this reduces the cost of a kernel entry/exit
(invalid syscall) from 465.1ns to 463.8ns.
Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/If4dc3501fd4e4f287322f17805509613cfe47d24
---
arch/arm64/kernel/syscall.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index e4c0dadf0d92..f533e83fd722 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -123,7 +123,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
local_daif_restore(DAIF_PROCCTX);
user_exit();
- if (system_supports_mte() && (flags & _TIF_MTE_ASYNC_FAULT)) {
+ if (IS_ENABLED(CONFIG_ARM64_MTE) && (flags & _TIF_MTE_ASYNC_FAULT)) {
/*
* Process the asynchronous tag check fault before the actual
* syscall. do_notify_resume() will send a signal to userspace
--
2.29.2.299.gdc1121823c-goog
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next reply other threads:[~2020-11-18 3:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-18 3:20 Peter Collingbourne [this message]
2020-11-18 11:23 ` [PATCH] arm64: mte: optimize asynchronous tag check fault flag check Catalin Marinas
2020-11-18 16:53 ` Peter Collingbourne
2020-11-18 17:07 ` Catalin Marinas
2020-11-18 17:48 ` Catalin Marinas
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